1. Field of the Invention
This invention relates to part of a process for the manufacture of dental prosthetic items in a dental CAD system. In the dental CAD/CAM system “CEREC” (registered trademark of Sirona Dental Systems GmbH, Germany), the operator performs a 3D scan of a prepared tooth and its adjacent teeth, from which scan a data representation of the 3D model of the region scanned is produced in the memory unit of a computer and displayed.
2. Description of Related Art
In order to copy, say, the chewing surface of a tooth prior to preparation, the tooth can be scanned prior to preparation, together with the adjacent teeth, and a corresponding 3D model can then be computed.
Another variant comprises the scanning of an impression of the opposite jaw, in order to achieve an optimum fit of the dental prosthetic item on said opposite jaw.
In order to be able to use the information of the unprepared tooth or the impression of the opposite jaw, it is necessary to achieve a sufficiently exact geometric alignment of the corresponding models to the model of the prepared tooth. The information that makes such alignment possible must therefore be contained in the models.
The use of the surface of the adjacent teeth, with no change in the surface between the scans, is known in the prior art. This normally takes place automatically via the software, by means of which regions of the 3D data set corresponding to each other are sought and found.
There are cases in which this automatic process fails, due, for example, to the poor quality of the scans, too few unaltered parts of the 3D models, or interfering image components such as cofferdams or rolls of cellulose wadding.
Despite this, and in order to be able to use this information either from the scans prior to preparation or from the opposite jaw, the position match of the models must be obtained in a different way.